1. Field of the Invention
The present invention relates generally to Ethernet systems and methods and, more particularly, to a system and method for auto 10BASE-T/10BASE-Te selection based on cable characteristics.
2. Introduction
The 10BASE-T standard defines transmission at 10 Mbit/s over twisted pair cabling. 10BASE-T transmission requires only two wire pairs to operate. While further IEEE standards have been defined for higher transmission speeds (e.g., 100 Mbit/s 1 Gbit/s, 10 Gbit/s, etc.), physical layer devices (PHYs) that support 10BASE-T transmission remain prevalent in the field. This is due at least in part to the rapid rate of increase in transmission speeds relative to the slower rate of increase in needed application bandwidth. The resulting disparity between bandwidth supply and bandwidth need dictates that 10BASE-T usage will continue far into the future.
A recent emphasis in Ethernet transmission system development is energy efficiency. This emphasis is in response to the continuing escalation of energy costs associated with Ethernet transmission systems. The increase in transmission rates has resulted in a corresponding increase in energy costs. Such being the case, various industries have become increasingly sensitive to the impact of those rising energy costs. Many companies are now looking at their IT systems' power usage to determine whether the energy costs can be reduced.
IEEE 802.3az is the result of such an industry focus and seeks to address the rising costs of IT equipment usage (e.g., PCs, displays, printers, servers, network equipment, etc.) through the usage of Energy Efficient Ethernet (EEE) networks. Included within such an effort is a mechanism to reduce the power consumed by a PHY during 10BASE-T transmission. This lower-power version of 10BASE-T transmission, which is referred to as 10BASE-Te, serves to reduce the voltage levels of the PHY. More specifically, a PHY operating in a 10BASE-T operating mode is designed to have a peak differential voltage on the transmitter circuit when terminated with a 100Ω resistive load of between 2.2V and 2.8V. In contrast, a PHY operating in a 10BASE-Te operating mode is designed to have a peak differential voltage on the transmitter circuit when terminated with a 100Ω resistive load of between 1.54V and 1.96V. This reduced peak differential voltage on the transmitter circuit represents a reduced voltage envelope, which leads to a corresponding reduction in the power envelope. The lower voltage also eliminates the need for higher voltage rails in the system or on the chip. These higher voltage rails would require costly voltage converters, which can also have associated energy inefficiencies. These inefficiencies are multiplied in multi-port systems.
The reduction in voltage serves to reduce the power consumed by the PHY when operating in the 10BASE-Te operating mode as compared to the 10BASE-T operating mode. As noted above, 10BASE-T/10BASE-Te usage is expected to continue far into the future even though the 10 Mbit/s transmission speed can be considered obsolete. PHYs that incorporate both 10BASE-T and 10BASE-Te operating modes will therefore be deployed in networks comprised of existing cabling infrastructure. What is needed therefore is a mechanism that enables auto configuration of PHYs that incorporate both 10BASE-T and 10BASE-Te operating modes during installation.